The forming of shapes or openings in moving strip sheet material has usually been confined in the past to forming longitudinal formations by what is called roll forming. Various different methods have been proposed for forming openings, or transverse formations, in moving strip material. In simple cases, a series of stationary presses are located along a production line and a piece of strip material is moved along in a start-stop fashion. Every time the material stops in registration with a press, the press closes and makes a formation after which the press opens and the material moves once more. However, these systems are relatively slow, since the material must stop at each press, and start again, for each formation.
Another system is the use of flying dies. These flying dies are somewhat similar to flying shears used in roll forming of continuously moving strip material. Various forms of piercing or forming dies can be placed on a flying die apparatus, and the strip material can move slowly through the flying die apparatus. By suitable movement mechanisms in the die apparatus the dies are first of all accelerated up to the speed of the moving material. And they are then closed on the material while the material is moving. The dies must then be opened again and returned to their starting position.
This system again is relatively slow, since the flying die apparatus must move forwardly and backwardly along the axis of the moving sheet metal in a repetitive manner.
Certain improved systems for rotary forming are shown in U.S. Pat. No. 4,732,028, dated Mar. 22, 1988, inventor E. R. Bodnar.
In this system two rotary die carriers are provided with a plurality of separate die supports each having dies mounted on the supports. There are upper and lower dies, to operate on both sides of the sheet of metal, and the upper and the lower rotary carriers had to be carefully synchronised to ensure that each pair of dies are closed and opened on the sheet of metal in precise registration. However, this system required that each of the die supports be rotatable relative to the rotary carriers. Consequently, some form of guide means had to be provided to guide the rotary die supports so that they came into registration with one another, and just prior to closing on the metal and remained in registration until they had opened again.
The system provided die support guides which guided the leading and the trailing edges of each die support by means of guide pins and end guide cams for guiding the pins so as to ensure such registration. The end guide cams were located at opposite ends of the die carriers. One guide cam guided the leading guide pins and the other guide cam guided the trailing guide pin, of each die support. This arrangement was therefore relatively complex to engineer and build.
Another of the problems with this system was that when the system was used for piercing openings in the sheet of metal, the blanks or slugs or a sheet of metal which had been removed from the opening tended to remain in the dies, and there was some difficulty in ensuring that they were removed.
The die carriers themselves were rotatably mounted on bearings at each side of the carriers, and were suitably driven through gear means known in the art. However, the die supports were supported in generally semi-cylindrically shaped transverse grooves formed along the length of the die carriers, and it was found to be somewhat of a problem to both lubricate the semi-cylindrical grooves and at the same time keep them free of dirt and other contaminants.
A still further problem associated with the earlier apparatus described is the problem of matching the rotary movement of the dies with the linear movement of the workpiece. The linear movement of the workpiece is constant and unchanging. However, it is obvious that the rotary movement of the die supports, and their dies, causes their linear speed to go through a slight change from a point just before contact with the workpiece, and during contact, and to a point just after contact with the workpiece where the dies separate once more.
During dead centre contact, the dies are clearly moving at the same linear speed as the sheet metal strip workpiece, and for that instant, in the same linear direction. However, just before the dies contact the workpiece, they are still moving angularly towards the workpiece. The linear speed of the two dies at this point is thus slightly less than the linear speed of the workpiece.
Similarly, after closure, as the two dies start to separate from the workpiece, their linear speed relative to the workpiece tends to slow down.
This effect is of little importance where the workpiece is thin, and where the depth of the formation is relatively slight. However, with a thicker workpiece or where the depth of the formation is greater, then the reduced speed of the dies before and after closing relative to the workpiece, will either damage the workpiece or the dies or both. As a result, some attempt must be made to accommodate a linear translation of the dies relative to the workpiece so that they can temporarily speed up just prior to closing and speed up again just after opening.
For all of these reasons, it is desirable to provide a rotary apparatus for forming continuously moving strip sheet material in which the design and operation of the die supports and the die carriers is improved and the problem of contamination and lubrication is removed, and in which the problem of knocking out the slugs is improved, and in which the problems relating to the matching of the speed of the dies with the sheet material is solved, and in which the guiding of the die supports is carried out in a simpler and more effective manner.